
$. 



y<9r\ 



INDUSTRIAL EDUCATION 



NOTES ON MECHANICAL DRAWING 



By 
ROLLAND S. WALLIS 




A SUPPLEMENT TO THE DRAWING COURSES 

CONDUCTED BY THE 

ENGINEERING EXTENSION DEPARTMENT 



COPYRIGHT, 1922, BY THE 



ENGINEERING EXTENSION DEPARTMENT 

IOWA STATE COLLEGE 

AMES, IOWA 






iCI.AI>77tfl2 

JlfN 



< s^ 



Notes on Mechanical Drawing 

By HOLLAND S. WALLIS 

Drawine is a medium of expression necessary to the engineer By 
its^sX is enabled to present the details of his ideas far more effect 

! tl, n „ eonld be done by description in words. In fact, it would 
SnisTtpel s" undertakiiig to attempt the written description 
of a complicated machine so that it could be accurately reproduced by 
a workman. 



LJf^ 




1 * 

1 

! 


(b) 






<: — 












K 








\ 


f 



<-4 

2" 


'1 



(aj 



Block 

Two Req'd -Cast Iron 



Fig. 1. 



-An artist's sketch (a) and a working drawing (b) 



An artist's sketch (Fig. la) is of value m presenting general ideas, 
but the demands made on the technical draftsman are much more ex- 
acting He must show with mathematical exactness the shape and the 

enters and with the necessary lines and figures added to show the 

"luXSiniar: Sly made to scale and executed with drafting 
instruments. Strictly speaking, all drawings made with mstenments 
may be termed mechanical drawings, but the term is generally taken 
to refer to engineering or working drawings. The technical drafts- 
man represents by means of outline drawing, making little or no use of 
shading to represent depth or relief. . 

The ability to read drawings is vital to all connected m any way 



with technical industry, while the added ability to execute such draw- 
ings neatly and quickly is as essential to an engineer as is a knowl- 
edge of practical mathematics. 

Requirements of a Good Draftsman. — A good draftsman is neat and 
accurate and works rapidly. Neatness in drafting includes the ar- 
rangement and finish of line work and lettering, as well as cleanliness. 
Accuracy can be attained by care in the use of the scale and by keep- 
ing pencil points and drafting instruments in proper condition. Speed 
is desirable up to the point where it conflicts with neatness and ac- 
curacy. It may be attained by systematic procedure in all routine 
operations. 



Drawing Instruments and Materials 

Selection of Drawing Instruments. — The beginner is cautioned 
against the common error of purchasing cheap tools, as this is mistaken 
economy. A satisfactory quality of materials and workmanship neces- 
sarily means increased cost over inferior instruments which are worth- 
less for accurate work and expensive at any price. There is usually 
enough to occupy the mind of a beginner without the perpetual annoy- 
ance attending the use of poor tools. 

The assistance and advice of an experienced draftsman will prove 
valuable in the selection of drafting instruments and supplies, as the 
differences in material and workmanship are usually not readily ap- 
parent to one not accustomed to handling them. Small variations 
from the sizes given in the suggested list are permissible. 

The Necessary Outfit. — The following instruments and materials 
will be required by the student : 

Set of drawing instruments, including : 

Compasses (6-inch) with extension bar, fixed needle-point, and re- 
movable pen and pencil-points. 
Dividers (5%-inch) 
Ruling pen (5-inch) 
Bow pencil 
Bow pen 
Bow dividers 
Drawing board (16"x22") 
T-square (24-inch) 
Triangle (45°, 6-inch) 
Triangle (30°-60°, 9-inch) 
French curve 

Architects 1 scale (12-inch, triangular) 
Engineers' scale (12-inch, triangular) 
Thumb tacks 
Drawing pencils (II and 81 1) 



Drawing paper (H"xl5" sheets, white) 

Pencil eraser (Fabers "Ruby," No. 112, or equivalent) 

Cleaning eraser (or "Art-Gum") 

Pencil pointer (6-inch flat single-cut file, or sand-paper block) 

Drawing ink (Black, waterproof) 

Penholder and lettering pens (See chapter on lettering) 

Dusting brush or cloth 

Penwiper 

Erasing shield 

Drawing Board. — Drawing boards are made of soft wood, usually 
white pine or basswood, free from knots and with the upper surface 
dressed to a true plane surface. To prevent warping they are made 
of narrow strips of wood glued together, commonly with their ends 
set into end pieces (Fig. 2a). Large boards should be provided with 



^-5aw Cuts 

. -Pnawing Board 




Fig. 2. — Drawing Boards. 

cleats so fastened that the wood of the board is free to expand or con- 
tract. Saw cuts made with the grain and part way through the board 
from the back (Fig. 2b) further reduce any tendency to warp. 

The working edge, along which the head of the T-square is operated, 
must be smooth and straight. This edge should be marked for easy 
identification, and always kept at the left of the draftsman. 

It is convenient to raise slightly the far edge of the board by means 
of a suitable block (Fig. 2c), but the inclination should not be enough 
to cause the T-square to slide down or pencils to roll. Large drawing 
boards are often supported on wooden horses or folding stands of 
various sorts. 

Large drawings are frequently tacked directly to the drawing- 
tables instead of to separate boards which are expensive and awkward 
to handle in large sizes. Such tables have tops of soft wood, these be- 
ing either horizontal or adjustable as to inclination. 

Some draftsmen find it convenient to keep either the far or the near 
edge of the drawing board straight and at right angles with the work- 
ing edge, so that long vertical lines may be drawn with the aid of the 
T-square. This is not good practice except for lines (such as border 
lines) which do not affect the accuracy of the drawing itself. 

T-Square. — The T-square (Fig. 3b) consists of a thin blade rigidly 
attached to a head, preferably at right angles with its working edge. 
While commonly made of wood, they are also obtainable with steel 



blades and cast-metal heads. Wood blades with transparent celluloid 
edges (Fig. 3d) are popular. 

There are two working edges (Fig. 3b)— the sliding edge on the head 
and the drawing edge on the blade. While the lower and upper edges 
of the blade are usually parallel, the lower edge should not be used 
as a working edge. The drawing edge serves as a guide in drawing 
horizontal lines (the pencil moving to the right as indicated in Fig. 4)°, 
and as a support for the triangles. 



Working Edges 




Blade 



(b) Celluloid Reinforcing Strip'' 

af End of Blades 



r 


(d) Celluloid Edges ( e i 


• 


' 1 


u 


(f) 



Fig. 3. — T-squares. 



Either an extra swivel head (Fig. 3a) or an adjustable blade (Fig. 
3c) are convenient in work involving many parallel lines at odd angles. 
The micrometer screw in the head of the latter style offers a convenient 
means of trueing up the blade to agree with the drawing. 

T-squares with long blades are best made in the "English" pattern 
(Fig. 3f ) with the blade widest near the head, and the head with its 
greater portion above the working edge of the blade. This style has a 
good balance and a longer lever arm to hold the blade in position. 

Drawing boards or tables may be fitted with some one of the various 
parallel-blade attachments, and the necessity of using a T-square thus 
done away with. These are combinations of strings, wires, pulleys and 
clamps so arranged as to keep the blade at all times parallel to its or- 
iginal position as it is moved up or down by the draftsman. 

Triangles.— Drafting triangles are made of wood, hard rubber, cellu- 
loid or steel. Those constructed of wood are clumsy, soon become in- 
accurate due to loosened joints or warping, and are easily damaged. 
They have the advantage of being light and cheap, but are no longer 
in common use. 

Hard-rubber triangles, while light and relatively cheap, are brittle 
and easily chipped or broken. Steel triangles are accurate, but they 
are^ expensive, apt to soil or cut the drawings, and easily tarnished. 

Celluloid triangles are almost universally used at the present time. 



They are light, strong, flexible, nearly transparent easily trued up, 
and show little tendency to warp if properly cared tor. 

The 45° and the 30°-60° triangles are used separately along the up- 
per edge of the T-square as indicated in Fig. 5. Lines are correctly 




Fig. 4.-Relative positions of drawing board, T-SQuare and triangles. 



drawn along the triangles only in the directions indicated by the ar- 
row™ that is, always away from the body and to the right. The lines 
which may be drawn with the 30°-60° triangle are shown combined m 
Fig. 5j and those with the 45° triangle in Fig,5k, The triangles may 
also be used in combination (Fig. 6) to obtain lines at 15 and 75 
with the horizontal and the vertical. 




(h) (i) <j> ^^'"W - 

Fig 5.— The triangles used separately. 

Lines parallel to any given line may be drawn conveniently by bring- 
ing one edge of a triangle to coincide with the line, and then placing 




Horizontal-' / i \ 



(h) (I) (J) 

Fig. 6. — The triangles used in combination 



Pora/le/ Lines 



-Perpendicular 
Line 



, ,- Perpendicular 




-Fixed Triangie 
or Straight Edge 



'--Fixed Triangle 
or Straight Edge 



1 - Fixed Triangle 

or Straight Edge 

(a) (b) (c) 

Fig. 7. — Drawing parallel and perpendicular lines with the triangles. 




Fig. 8. — Some special triangles 



the other triangle or any straight-edge against either remaining edge 
of the first triangle (Fig. 7a). The second triangle is held fixed for 
the first to slide along to the desired position. The correct method of 
drawing a line perpendicular to any given line consists in bringing the 
hypotenuse of either triangle to coincide with the given line, the other 
triangle or a straight edge being placed in a fixed position in contact 
with the first (Figs. 7b and 7c). The first triangle is then reversed 
and the line drawn along the new position of its hypotenuse. 

Several special triangles have been devised to take the place of the 
two standard triangles. The "Kelsey" triangle (Fig. 8a) is a very 
convenient instrument, and may be obtained with the under face grad- 
uated as a protractor. The "Zange" triangle (Fig. 8b) is designed to 
permit drawing all the 5-degree angles from 5° to 90°. The "Rondin- 
ella" triangle (Fig. 8c) combines the angles of the ordinary triangles 
with the addition of the 67%° and 22%° angles. An adjustable angle 
(Fig. 8d) is an inexpensive instrument and a decided convenience on 
odd-angle work. 

Drawing Paper. — Drawing paper may be purchased in a large var- 
iety of qualities, tints, and surfaces, either in sheets or in rolls. The 
best hand-made paper is made in sheets only, and in; the sizes listed 
in the following table. The symbol (*) indicates the sizes commonly 
obtainable in sheet papers. 

Cap ; 13"xl7" Super Royal 19"x27" 

Demy 15"x20" imperial 22"x30" 

Medium 17"x22" ^Double Elephant 27"x40" 

*Royal 19"x24" Antiquarian 31"x53" 

Manilla papers of buff tints in sheets or in rolls are very commonly 
used for detail drawings intended to be traced on cloth for blueprint- 
ing. White papers of smooth surface are desirable for drawings that 
are to be inked. 

A sheet of drawing paper correctly placed on the drawing board 
(Fig. 4) should be near the working edge of the drawing board so as 
to utilize the most rigid part of the T-square blade, and should be kept 
well away from the lower or near edge of the board in order to avoid 
the necessity of using the T-square in the extreme position indicated 
by dash and dot lines (Fig. 4). In this position it is apt to be unsteady, 
as the corner of the board is usually worn and inaccurate, and as only 
about half of the head bears against the board. 

To fasten the sheet of paper to the board, a tack is first placed at 
"A." The T-square is then moved to the upper edge of the paper and 
this edge swung into line by grasping the paper at "C." A tack is 
placed at ''"C" and the sheet stretched slightly by pushing toward "B" 
and "D" with the palm of the hand, tacks being placed at these cor- 
ners in turn. Thumb-tack holes should be kept outside of the trim 
lines (Fig. 4) of the finished drawing. 

Thumb Tacks. — The drawing paper is fastened to the board or table 
by means of thumb tacks. The better grades are made of brass, Ger- 



man-silver or steel, usually with sharp, steel pins riveted or screwed into 
the heads (Figs. 9a and 9b). They should be thin, especially at the 
edges, so as to offer little obstruction to the T-square, and should be so 
constructed that the pins will not push through. 






e 



t^ nr 



(a) 



(b> 



(c) 



(d) 



Fig. 



-Thumb tacks. 



(e) 



A cheap and widely-used style of thumb tack (Fig. 9c) has the head 
and the point punched from the same piece of soft steel. The "Univer- 
sal" tack (Fig. 9d) is turned from one piece of steel to a very thin edge. 
To protect the edge this tack is removed by a special puller (Fig. 9e). 
Tacks should be pushed straight into the board so as to present the 
minimum obstacle to the T-square. 

Drawing* Pencils. — Drawing pencils are manufactured in various de- 
grees of hardness grading from very hard to very soft as follows : 9H, 
8H, 7H, 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B. 

Considerable variation may be found in comparing the hardness of 
the same grades in different brands. The proper degree of hardness 
depends upon the surface of the paper, the atmospheric conditions, 
the nature of the work and the whim of the draftsman. It is advisable 
to use the softest pencil that can be made to do satisfactory work, as 
the resulting drawings are clearer and easier to ink or trace, while 
erasures and changes are easier to make than when the pencil is so hard 
as to cut into the surface of the paper. 

Drawing pencils are usually made without eraser tips, and hexagonal 
to prevent rolling. They may be sharpened either to a long conical 
point or a flat chisel point. The chisel point has certain advantages in 
penciling lines where accuracy is especially desired, as the wear is so 
distributed as to lessen the need for frequent sharpening, and as the 
point can be kept close against the straight edge. 

The conical point is generally preferred and its use is recommended. 
Such a point is easily and quickly formed and is suitable for lettering 
and general use as well as for line work. Ordinary pencil sharpeners 
can be used, though they give rather too short a bevel for drafting 
purposes. The wood should be cut away at a uniform taper to a dis- 
tance of about I'/i" from the point so as to leave about %" o\' lead lo 



be tapered to a uniform conical point. Carefully sharpened pencils 
are a necessity in neat and accurate drafting-. 

The conical point can be handled with a minimum amount of sharp- 
ening if inclined about 45° (Fig. 10a) so that wear comes on the side 
of the point. Then, if the pencil is rotated in the fingers as lines are 
ruled, this wear will be evenly distributed on all sides of the point. The 
pencil point should be kept close into the angle formed by the paper 
and the vertical face of the guiding straight-edge (Fig. 10a). 




15° to 30' 




Offset ( b ) 
Fig. 10. — Ruling- positions for drawing pencil and pen. 



Neatness and speed in penciling may best be obtained by doing all 
blocking out in very lightly penciled lines. These lines are necessarily 
indefinite in length. As soon as the necessary intersections are ob- 
tained, the portions of these lines needed are strengthened by tracing 
over with more pressure on the pencil. Do not erase the light lines not 
needed. If drawn ligiitly they will not be distinct enough to confuse 
the drawing. The less erasing that is done, the more rapid and neat 
will be the drafting. 

Erasers. — Erasers are needed by the draftsman for cleaning and for 
erasing. Cleaning rubber is very soft, and may be used to clean inked 
drawings without injury to the inked lines. Art gum, although 
"mussy, " is frequently used for this purpose. 

The so-called ink erasers should have no place in the draftsman's 
outfit, as their use results in injury to the surface of the paper or trac- 
ing cloth, making it impracticable to ink over the erased portion neat- 
ly. Ink lines are best removed by the use of a pencil eraser (such as 
Faber's "Ruby" No. 112), as these erasers (while slower) leave the 
surface of the drawing in good condition. 

In an emergency a sharp pen-knife may be used as a preliminary 
operation in erasing ink lines, but this practice is not a good one, as the 
surface of the drawing is almost invariably injured. 

Pencil Pointer. — Pencil pointers are used to sharpen accurately the 
lead of the drafting pencil. The usual type is a small block built up of 
sheets of fine sandpaper, but a small flat file is better. 



10 



Erasing Shield.— An erasing- shield (Fig. H) i s a very thin piece of 
sheet metal, celluloid or cardboard, having various small openings of 




Sw/n 




Fig. 11. — Erasing shields. 

different sizes and shapes. In use it is so placed on the drawing as to 
confine the erasure to the part to be erased. 

Ruling Pen. — Ink lines of uniform thickness are obtained by the 
use of a ruling pen moved in contact with the edge of a straight-edge, 




(a) (b) (c) 

Fig. 12'.— Ruling pens. 

triangle or French curve. The usual pattern is indicated in Fig. 12a, 
both a front and side view being shown. 

When the spring-blade is released such a pen will open as shown in 



11 

Fig. 13a. Various quick-opening devices which facilitate the cleaning 
of the pen nibs are shown in Fig. 13 (b to g, inclusive). Each style 
has certain merits and each is more apt to get out of order than is the 
plain pen. 




Fig. 13. — Various ruling pens opened for cleaning. 



The width or weight of the line produced depends on the distance be- 
tween the nibs or points, this distance being adjusted by the thumb 
screw. The pen should be held in a vertical plane containing the 
line being ruled, and with the top inclined in the direction of motion 
(Fig. 10). There should be a space between the ruled line and the edge 
of the straight edge. This offset (Fig. 10b) is necessary to prevent 
blotting the ruled lines, as the ink will run under the ruling edge if 
allowed to come into contact with it. Lines are ruled with a free-arm 
movement with the finger tips resting on the T-square blade. When 
near the end of the line the hand is stopped and the balance of the line 
ruled with a finger movement. 

To give good results the points or nibs of the ruling pen must be kept 
sharp. If the worn ends are easily visible when held up to the light 
the pen should be sharpened. This process includes two operations. 
The nibs are screwed together till they touch, and the ends re-shaped 
on a fine oilstone by a motion as of ruling lines backward and forward. 
This dulls the ends of the nibs. The nibs are then separated, and each 
brought to a thin invisible edge by carefully rubbing the outside sur- 
face of each nib on the oilstone. 

Due to its larger ink capacity the "detail" or "Swedish" type of 
ruling pen (Fig. 12b) is of value in inking long and heavy lines. Extra- 
heavy lines may be ruled with little danger of blotting with a pen 
having a central nib (Fig. 12c) which increases the capillary capacity 
for ink without interfering with the action of the outside nibs which 
define the width of the line ruled. 



12 

Ruling pens are filled with ink by inserting the quill of the ink bottle 
between the nibs, care being taken to see that no ink is on the out- 
side of the nibs. 

Dividers. — Three types of dividers or "spacers" in common use are 
illustrated in Fig. 14. In addition to the original pattern (14g) are 
shown the cylindrical (14h) and the "Richter" pattern (14i), the dis- 
tinguishing features of the latter being the flattened legs and the easily 
interchangeable points. This instrument requires good workman- 
ship in that the pivot joint must work smoothly and with uniform fric- 
tion, while the points must be long, sharp and of equal length. 




x& 



Start circle here 

(e) 

-Use this end r s, - ^- - , n <_ 

of needle point x p~--~e--' 



(a) (b) (f) (g) (h) (i) 

Fig. 14. — Compasses and dividers. 



Dividers are used (1) for transferring unmeasured lengths or dis- 
tances from one part of the drawing to another, (2) for stepping off 
any number of equal spaces and (3) for dividing any given length of 
line into a required number of equal spaces. 

The second use should be avoided, where possible, due to the multi- 
plication of any slight error made in setting the instrument to the re- 
quired distance. If possible to scale off the distance first and then sub- 
divide (the last use mentioned), this error will be eliminated. As an 
illustration of the method of subdivision let it be required to divide the 
line rm (Fig. 14f) into four equal parts. The dividers are set to a 
trial spacing om and the legs swung alternately in opposite directions, 
as indicated, until point s is reached. The total error is the distance 
rs, and the error of setting is one-fourth of this, or xs. The correct set- 
ting, then, is xp. The dividers should be set to this distance as accu- 
rately as possible and the operation repeated until the setting is proven 
correct by actual trial, when small punctures may be made in the 
paper to indicate these divisions. 

Great care should be taken not to dull, bend or break the points of 
this instrument, as its value depends on their condition. When neces- 



13 

sary to sharpen them the outside surfaces of the points should be rubbed 
on a fine oilstone. 

Compasses. — The large compasses are used for drawing circles and 
circular arcs in pencil or ink, and are made in the same styles as the 
dividers. In the ordinary style (Fig. 14a) the pencil-point may be re- 
leased by the clamp screw at y and replaced by a pen-point or leg, as 
has been done in the "Richter" type (Fig. Me). Always use the 
shoulder end of the needle point (Fig. 14b), adjusting it as indicated 
in Fig. 14c. A good style of flat point for the compass lead (Fig. 14d) 
is readily formed with the aid of a small flat file. 

When in use the two legs of the compasses should be bent at the 
joints v and w (Fig. 14a) to a vertical position, as illustrated in Fig. 
14e. This avoids any unnecessary enlargement of the puncture made 
by the needle point, and also permits the nibs of the pen to bear evenly 
on the paper. 

Bow Instruments. — The convenience and increased accuracy ob- 
tained by the use of small bow-dividers and compasses make them a 
necessity to the draftsman. Separate compasses are provided for pen 
and pencil work — the bow-pen and the bow-pencil. A set of bow instru- 
ments of the common type is shown in Fig. 15 (a, b and c). 





Fig. 15. — Bow instruments. 



The advantage of quicker adjustment is claimed for the ''center- 
screw" pattern (Fig. 15d), due to the double travel of the adjusting- 
screw. As a matter of fact this is hardly the case, as the draftsman in 
changing the setting of the usual type pinches the ends together and 
spins the adjusting-screw into the approximate position desired, thus 
saving time and reducing the wear on the screw and threads. 

The "hook-spring" pattern (Fig. 15e), if well made, has a somewhat 
more uniform spring tension, but most draftsmen iind the position of 
the adjusting screw an awkward one. 



14 

Scales. — Scales for measuring and laying off distances on drawings 
are usually constructed of boxwood, preferably with the graduated 
edges covered with white celluloid. In Fig. 16 are shown cross-sections 
of the usual types of scales, all but (c) being of wood with or without 
white edges. The exception mentioned is made of steel and graduated 





(c) 



xy^y^<^. 


^////// <<y////^ 


(d) 


(2) (f) 


Fig. 16.- 


—Forms of drafting scales. 



on the two upper faces. From the standpoint of economy the six-scale 
faces of (a) and (b) are an advantage, but in use such scales are in- 
convenient and confusing, as they must be turned more or less to pre- 
sent the desired edge, and as there exists a strong chance for the care- 
less use of the wrong scale. 

The "improved" form of the triangular scale (Fig. 16b) presents 
the edges at a better angle for easy reading but concentrates the wear 
on the sharp edges of the scale — this soon rendering the scale practi- 
cally useless. Of the flat shapes (e) is probably the best. It has two 
scale faces as has (d), but it is easier to pick up and to hold, and has 
only one scale in view at any time. The form shown at (f) has four 
scale faces, is convenient to use, and in the 6-inch length is a popular 
vest-pocket style. 



r Mi " [ T" llM T" ll ' tl T^ i "T ,l ^ M r^""r\ 



« v. <n 



wLLLLLU 



(a) 



~~d 1 1 1 4 5 W 



X \\L\\\\\\A 



\ i \ 






(b) 

Fig. 17. — Triangular scales. 

Scales may be "open" (Fig. 18) or "full" (Fig. 17a) divided. The 
"civil engineer's" scale (Fig. 17a), used in map drafting and graphical 
analysis, has inches divided into 10, 20, 30, 40, 50 and 60 equal parts, 
while the "architect's" or "mechanical engineer's" scale (Fig. 17b) 



15 

usually carries a natural scale of inches into sixteenths, with the other 
scales divided into various equal lengths, each being considered as rep- 
resenting a foot and each such length being divided into 12 parts repre- 
senting inches. Thus, on the lower scale in Fig. 17b, either %" or 1" 
may be taken as representing one foot on the drawing. 





< 

k- 


2 

-/V/-- 


-64"- 


■:-1 

I 




\ * *> * a 




\ 

Y 


\ 


W 


fl 


/ 6 9 £ 

1 UjJjJjJjjjJ.di.lJ 




I 

1 


Z 

1 


II 



Fig. 18. — Reading a scale. 

In Fig. 18 is indicated the method of laying off or reading dimensions 
with an architect's scale, the scale in use being known as the "inch 
and one-half scale." This scale is stated on a drawing as 1%"=1' — 0". 
The terms "half -size" and "quarter-size" are frequently used also, and 
mean 6"=1'— 0" and 3"=1'— 0", respectively. 

French Curves. — French (or "irregular) curves are used to guide the 
ruling pen in inking non-circular arcs. They are made of wood, hard 
rubber, or transparent celluloid — the latter material being preferred 
on account of its transparency, flexibility and durability. They are 




Fig 



French or "irregular" curves. 



made in a large variety of shapes, a few of which are illustrated in 
Fig. 19. The general type known as "ship" curves (a) is frequently 
valuable on account of the flat curves they carry. A curve of con- 
siderable practical value is known as a "logarithmic spiral" (f). 

A curved line is usually determined on the drawing by a series of 
points. A freehand line should be drawn lightly through these points 
and a suitable part of the French curve fitted carefully to this line so 



16 

as to contain at least three points. This portion of the line may then 
be drawn, it being' best, however, to stop short of the distance the curve 
seems to fit. Then the curve is shifted along to include one or more 
additional points, and the line continued. In inking against a curve 
the left end should] always be inked first, working towards the right. 
The ink line can be more accurately formed in this way as the junc- 
tions are at the left of the pen nibs instead of beneath it. 

Drawing Ink. — Most engineering drawings are inked or traced with 
black India ink of the waterproof variety. This ink was introduced 
when inked drawings were more generally used, as with ordinary ink 
a little moisture was apt to smudge a drawing badly. Now that trac- 
ings seldom leave the drafting room except for blue printing the use 
of waterproof ink is not strictly necessary, and some draftsmen prefer 
to use the ' ■ general ' ' drawing ink. 

Drawing ink is usually purchased in small bottles equipped with 
quill or glass fillers attached to the stopper. As drawing ink dries 
rapidly the stopper should be kept in the bottle except when the pen 
is being filled. 

Dusting Brush. — Every draftsman should have a wide brush to use 
in quickly freeing his drawing of dust and of the dirty rubber crumbs 
resulting from erasing. Its use will assist materially in keeping draw- 
ings clean. A dusting cloth should also be kept at hand with which to 
w r ipe the dust off of the T-square blade and triangles. 

Tracing Cloth. — Tracings subject to much handling should be made 
on tracing cloth, a finely woven fabric so treated as to surface it for 
the pen and to make it translucent. One side is finished glossy and the 
other dull. While the glossy side was originally intended for inking, 
the dull side is now customarily used. Among the reasons for this 
practice are the facts that the dull side takes ink and especially pencil 
work better ; is less disfigured by erasing ; is less trying on the eyes, 
especially under artificial light ; photographs better and lies better on 
the board. Tracing cloth is made in rolls of 24 yards, and in various 
widths and qualities. 

Before inking on tracing cloth a little powdered chalk or "pounce" 
should be rubbed into the surface with a chamois skin or the palm of 
the hand. This removes a slight greasy desposit characteristic of trac- 
ing cloth, thus making it take ink more readily. All excess of chalk 
should be wiped off carefully. Pencil lines (such as guide lines for let- 
tering) may be erased, when the inking is finished, with a soft rubber 
eraser or with a cloth moistened with benzine. All erasures necessary 
in connection with ink work should be made with a pencil eraser. A 
small piece of soapstone may be used to resurface the cloth after an 
erasure which roughens the surface. 

Tracing Paper. — Tracing paper is a thin and tough paper which for 
work of temporary character is a cheap and satisfactory substitute for 
1 racing cloth. Some of the tougher and thicker papers arc used as 



17 



drawing paper (blueprints being made from the inked drawings), while 
pencil drawings on the thinner sorts make satisfactory blueprints. 

Tracing paper is much used by architects for studies, as changes may 
be made and studied without erasing the original plan, a new sheet be- 
ing placed over the original sketch for each change considered. 

Extra Instruments 

The remainder of this chapter will describe various instruments 
which while not essential to the draftsman, are decidedly convenient 
on certain kinds of work. Most large drafting rooms have as a part 
of their equipment, an assortment of the rather unfrequently used m- 
struments-especially those costing more than the average draftsman 
cares to invest in instruments that are not to be constantly used. 




Fig. 20- — Standard protractor. 

The beginner should obtain copies of the trade catalogues of firms 
makin- drafting and engineering instruments and supplies, and should 
study these to familiarize himself with the nature of the various de- 
vices on the market. Space limitations make it impossible to list and 
describe all of them in this publication. 





(a) (b) 

Fig. 21. — Improved protractors. 

Protractor.— While not the most accurate method of measuring and 
lavin* out angles, the use of a protractor is one of the most convenient. 
There are manv types available, ranging from the common semi-circular 
tvpe (Fio- 20)' to precise instruments equipped with verniers, microm- 



18 



eter screws, and magnifying glasses for close reading. They are usu- 
ally made of brass or German-silver, but many excellent styles are now 
being made of heavy transparent celluloid, it being convenient to en- 




Fig. 22. — Movable-arm protractor. 

grave the graduations on the under side so that they are in direct con- 
tact with the surface of the drawing. Two improved patterns of the 
semi-circular type are shown (Fig. 21), as well as a good movable arm 




Fig. 23. — Full-circle protractor. 

type (Fig. 22) for the mechanical draftsman. In the plotting of sur- 
veyors notes the topographical draftsman usually finds the full-circle 
type (Fig. 23) convenient. 



19 



Beam Compasses.-This instrument (Fig. 24) is used when it is neces- 
sary to draw circular ares of greater radius than are possible with the 
ordinary compasses using an extension bar; and its use is advisable for 
smaller* ares where precision is necessary. This instrument consists 




Fig. 24. — Beam compasse 



essentially of a bar or beam on which may be clamped suitable attach- 
ments for holding the needle point and the pen or pencil points lne 
pen point (c) replaces the pencil point (d) in mkmg; and all these 
points, including the divider points (b), are interchangeable. A ser- 
viceable beam compass of cheaper construction is shown m *ig. te. 




Fig. 25. — A simple form of beam compasses. 

The beam compass is usually manipulated with both hands one 
steadying the needle point while the free end is moved with the other. 
Where the beam is very long the use of a rolling carr ler for the to 
is a convenience, and such an attachment may be obtained foi most in- 
struments. . , . -, ., _ 

Drafting Machines.— Various mechanisms have been devised to re- 
duce the constant moving about of triangles, scale and T-square. Prob- 



20 



ably the best of these is the Universal Drafting Machine, one type of 
which is shown in Fig. 26. Two sets of parallel arms permit the grad- 



/■ - Leveling Screw 




Fig. 26. — The "Universal" drafting machine. 

uated head to be moved to any portion of the drawing without rota- 
tion. The two interchangeable drafting edges (graduated with suit- 
able scales) always remain at right angles and parallel to their initial 




Fig. 27. — Home-made section liner 



positions. For angular work the two scales may be swung as one and 
clamped at any angle desired. Thus the use of triangles is not neces- 
sary, and lines may be drawn along the scale to any desired length in 
one operation. Variously graduated heads and scales are available 
especially suited to the class of work done by any draftsman. 



21 

Section Liners. — Considerable skill is required to space equally by 
eye such parallel lines as are used in cross-hatching or section-lining 
work, and a number of rather elaborate instruments have been devised 
to accomplish this spacing mechanically. Such devices are relatively 
expensive, and their use on ordinary work is hardly justified as a satis- 
factory degree of accuracy is within the ability of the ordinary drafts- 
man. Two home-made section-liners are illustrated in Fig. 27. The 
shaded pieces may be made of celluloid or wood, and one such piece 
must be made for each spacing desired. 



^ 




Z 



v - Celluloid or Hardwood 

Screw f/ook-~ s '' ni 

*r=s-^Cuf off flush 

^L_^ZEZZZZZZZZZlis7 ~7S 

(a) 



„ - Surface of Paper 

(b) 



>^ > l nn ] (>,n^l*'/>l<l<f"lM Z> 



Fig. 28. — A raised ruler for inking. (University of Illinois.) 

Raised Ruler. — Much time can be saved in inking by the use of a 
short ruler (Fig. 28) supported slightly above the surface of the draw- 
ing by four metal points. With this device wet ink lines may be worked 
over freely and little time need be spent waiting for the ink to dry. The 
construction is clearly indicated, and any draftsman can well afford to 
take the time and trouble necessary to make such a ruler. 



Spring Clips 




Fig. 29.— Ink-bottle holders. 



Ink Bottle Holder. — The main purpose of an ink-bottle holder is to 
give the bottle sufficient stability to prevent overturning it on a draw- 
ing. Two metal holders are shown in Fig. 29, as well as one (c) easily 



22 



constructed of cardboard. While the latter is not as heavy as the 
metal holders, its large base makes it difficult to overturn. 

Straight Edge. — A straight edge is a necessity in map drafting and 
similar work, and consists simply of a thin strip of wood or steel hav- 
ing two edges straight and parallel. Wooden straight edges (Fig. 30a) 
usually have hardwood or celluloid edges, while those of steel (Fig. 



(a) 



(b) 

Fig. 30. — Straight edges. 

30b) usually have one edge beveled for convenience in penciling. The 
straight edge is used for drawing long lines, and as a support for tri- 
angles and protractors. 

Proportional Dividers. — The operation of redrawing any drawing to 
a different size is facilitated (particularly when the scale ratio is an 
odd one) by the use of proportional dividers (Fig. 31). This instru- 




Fig. 31. — Proportional dividers. 



ment consists essentially of two equal legs pointed at both ends and 
opening on an adjustable pivot, the position of which determines the 
ratio of the end openings between points. Distances are taken off witli 
one pair of points and the other pair used to give the corresponding 
distance on the new drawing. 




Fig. 32. — A border pen. 



Border Pen. — Two parallel lines of equal or unequal weight may he 
readily ruled and duplicated by the use of a border pen (Fig. 32). Such 
a pen is also convenient for ruling parallel curved lines with the aid of 
;i French curve. 



23 

Railroad Pen. — This instrument (Fig. 33a) is intended for use in rul- 
ing two parallel lines representing the rails of railroad track, but it 
lias other uses as well. 

Curve Pens. — The curve or "contour" pen (Fig. 33b) is used for the 
freehand drawing of continuous curved lines of uniform width. The 
nibs are offset from the center line of the shaft which is free to rotate 
in the handle of the instrument. In use the curve is traced with the 




(»t mm 



= M 

V V 



ic-a 



(a) 



(b) 



(c) 



(d) 



(e) 



Fig. 33. — (a) Railroad pen, (b) curve pen, (c) double curve pen, (d) prickers, (e) drop pen. 



handle held vertically and the nibs trailing. To work best (on tracing 
cloth especially) the nibs should be kept sharp so that there is no tend- 
ency to slip sidewise. The double curve pen (Fig. 33c) is a great con- 
venience in drawing two freehand lines uniformly spaced, such as rep- 
resent roads and trails on maps. 

Pricker. — The most accurate results in transferring a distance from 
the scale to a drawing are attained when the points are marked by tiny 
punctures in the paper made by some sort of pricker (Fig. 33d), this 
instrument consisting simply of a fine steel point fixed in some sort 
of handle. The pricker shown at the left has a needle point screwed into 
place, while in the other the point is held by a small clutch and. may be 
readily replaced if broken. A satisfactory substitute may be made by 
forcing part of a fine sewing needle into a small piece of soft wood to 
serve as a handle. 



24 

Drop Pen. — Where a large number of small circles of equal size must 
be inked, the use of a drop or "rivet" pen (Fig. 33e) is convenient. 
The needle point is on the shaft "a" which is held in position by the 
tips of the thumb and forefinger while the rotating sleeve carrying the 
pen is spun around by an impulse from the second finger applied at 
"b." The pen is lifted slightly while the needle point is being moved 
to a new center. Some drop pens have a pencil point that can be in- 
serted in place of the pen, but most draftsmen draw the pencil circles 
freehand to save time. 

Railroad Curves. — Railroad curves (Fig. 34) are used for drawing 
the circular arcs representing track curves on railroad maps. Such 
curves differ from French curves in that the arcs are circular, being of 




\ ,'- Radial Line 

t (b) 

Fig. 34. — Railroad curves. 

the proper radius to represent one certain degree of curvature. Rail- 
road curves are made of cardboard, wood, hard rubber, celluloid or 
zinc, a set containing from ten to one hundred curves. Both curved 
edges are cut to the same radius, and each curve is marked with the 
radius in inches and the corresponding degree of curvature represented 
at the usual scale of 100 feet to an inch. 



Freehand Lettering 



The appearance of an engineering drawing depends largely on the 
quality and arrangement of the lettering placed on it by the draftsman. 
Lettering is not mechanical drawing, but it is essential that every 
mechanical draftsman have the ability to letter rapidly and neatly. 
This ability does not demand any marked artistic talent or any special 



25 

proficiencj 7 as a penman. Practice along the right lines will make any 
draftsman a good letterer, provided he always strives for a more perfect 
result. Careless practice is worse than none at all. 

The qualities most to be desired in the lettering of engineering draw- 
ings are legibility, neatness and speed. Legibility may be gained by 
adopting a simple style, such as the "Bernhardt," or "Engineering 
News" style, which is essentially that used throughout this text. Both 
legibility and neatness should follow a careful study of the letter forms 
and the correct methods of producing them. Speed, or the swing of the 
skilled draftsman, can only come with consistent practice. 

The chief object of this chapter is to give a good insight into the 
correct formation of such styles of freehand lettering as are in common 
use in the drafting-rooms of today. The essential thing to be gained 
here is an accurate knowledge of the shape of the letters studied and the 
proper methods of constructing them. 

Lettering is essentially freehand drawing. Mechanical aids in the 
formation of the various characters are the resort of the unskilled 
draftsman, and almost invariably result in lettering that is painfully 
inartistic. 

Single-Stroke Lettering 

The term "single-stroke lettering" does not mean that the complete 
le'tter is formed without raising the pencil or pen, but that only one 
passage of the pencil or pen point is needed to make each stroke used 
in forming the letter. 

Guide Lines. — The height of the letters is considered as being divided 
into five equal spaces. All the capitals are drawn full five spaces high, 
while the body parts of the small letters are made only three. Three of 
the six horizontal guide lines (Fig. 36) are usually drawn as indicated 
in Fig. 35. For practice purposes, and to save time and secure greater 
accurac3 r , it is convenient to use some sort of ruled paper. Various sorts 
of paper specially ruled for lettering are available, but a piece of Plate 
"A" profile paper answers the purpose nicely. On this paper each 
vertical quarter-inch is divided into five equal spaces so that it is 
convenient to draw the letters one-fourth of an inch high. It is best in 
studying the letter forms to draw them somewhat larger than is custom- 
ary on ordinary drawings. Guide lines should be drawn for all letter- 
ing. There are several lettering devices now available which make this 
operation a rapid and an accurate one. 

Slope of Lettering 1 . — Single-stroke lettering may be made either 
vertical or inclined. Both styles are in common use and most drafting 
rooms leave the choice to the draftsman. The vertical style of lettering 
is not used: so generally as the inclined style. This is due chiefly to the 
fact that the average draftsman can do better work with the inclined 
style, and his employer naturally desires the best appearing drawings 
that his drafting force is capable of producing. A common argument 
for vertical lettering is that uniformity is easier of attainment with 



26 

this style as there is only one vertical, while there are any number of 
slopes that may be used for lettering. However, the average draftsman 
soon demonstrates to his own satisfaction that slight irregularities in 
the slope given his inclined lettering are not so noticeable as are any 
departures from the vertical when the latter style is used. This is at 
least partly due to the fact that on most mechanical drawings the lines 
that are truly vertical are so numerous that the eye readily detects any 
deviation of the letter from the vertical. Inclined lettering has a slight 
advantage here in that it stands out better than does the vertical due to 
the contrast of the sloping characters with the horizontal and vertical 
lines of the drawing. 



I Units 



Slope Lines 




Guide Lines 



Fig. 35. — Method of drawin 



Sfctighf Edge 

lope lines for lettering. 



Some draftsmen, however, and particularly those that letter with 
the left hand, find that they can do better work with the vertical style. 
Then, too, nearly every draftsman will find occasions when it will be 
necessary for him to do some vertical lettering. One practice is to use 
the inclined lettering for notes, dimensions and general use, and the 
vertical style for reference letters, captions and titles. 

Lettering with the Pen. — Before a new lettering pen is used it should 
be placed in the pen-holder and the point held for a moment in the flame 
of a match. This treatment burns off the coating with which the pens 
are covered to prevent their rusting, and will be found to cause them to 
take the ink more 1 readily. Care should be taken not to draw the temper 
of the nibs by over-heating. 

The use of too much ink on the lettering pen is a very common cause 
of blots and poor intersections. Ever, and clear-cut ink lines require a 



27 

fairly light and even pressure on the pen point, together with frequent 
cleaning on a pen wiper. 

Steel Pens for Lettering. — The choice of the proper pen to nse for 
lettering depends on the draftsman's method of handling it as well as 
on the character of lines desired. Where there is a tendency to bear 
heavily on a pen one with stiff nibs is necessary, as the nibs should not be 
so flexible as to spread materially. Uniformity in width of stroke is 
essential, and such spreading tends to make the vertical strokes heavier 
than those made horizontally. Thus the character of the pen point 
should determine the weight of the strokes — not the pressure exerted on 
the nibs. 

The following list suggests an assortment of lettering pens, grading 
from fine to coarse : 

Joseph Gillott's No. 170 

Joseph Gillott's "Extra Fine/' No. 303 

Joseph Gillott's "F," No. 404 

Phinnev and Co.'s "Spencerian," No. 1 

Buxton & Skinner's "Cote Brilliante," No. 4 

Leonardt & Co.'s "Ball Pointed," No. 516F 
Spacing. — Beginners commonly space the letters of words too far 
apart and the words themselves too close together. The space between 
words and after commas should be sufficient to allow the insertion of 
a small letter "o" without crowding, while the space between sentences 
should be at least double this amount. Words placed too close tend to 
run together and thus confuse the eye of the reader. It should be kept 
in mind that placing the letters close together does not necessitate any 
cramping of the letter forms. The spacing between lines of lettering 
may vary from one-half to one and one-half times the height of the 
capital letters. 

Inclined Single-Stroke Lettering. — Inclined lettering may be drawn 
at various slopes, but a slope of 2 to 5 (about 68°) is recommended. 
Slope lines at this angle are easily obtained by constructing a right- 
angled triangle using 2 and 5 units as the legs (Fig. 35), and such 
slope lines should be drawn lightly whenever a note of any length is to 
be placed on the drawing. 

Inclined Capital Letters. — The study of the inclined capitals should 
proceed in the same order in which the letters are taken up in Fig 36. 
The completed form of each letter is given at the left, and the various 
strokes used in its construction indicated at the right. Note that the 
arrows give the direction in which each stroke is to be made, while the 
figures show the sequence of the various strokes. Most of the dash lines 
shown are slope lines (Fig. 35) which are parallel to the general slope 
of the lettering. 

In general, all strokes are made downward or to the right as the nibs 
of the pen are apt to stick into the drawing surface when strokes are 
made upward or to the left. At present most engineering lettering in 



28 



ink is done on tracing cloth, which presents a much smoother surface to 
the pen than does paper. For this reason it is often possible to simplify 
the construction of many of the letters so that fewer strokes are used than 



him' ~H^ m 




nm nn 





*#. 



i i 



I /\ I 




+Y-1r+ 



tf I /, 



MJh 



I I 



^ />/■/ fe 




rTTrTT^ 



> fe^ 



T mrFT r ~RTk 



^^^m 



I rK / 



/>r / 



^ — 7 — ■ 1 

Fig. 36. — Inclined single-stroke capitals 




&£ 



^3 



would be demanded by the rule just stated. In lettering- with the pen on 
rough paper it may be found advisable to subdivide some of the strokes, 
using as a guide the rules given. 

Two styles are shown for the capital "I." The simpler form should 



29 

be used except when the capital is followed by the small letter "1," with 
which this form of the capital is identical. 

The shape and construction of each letter should be carefully studied 
before practice is begun. In this way many mistakes may be avoided. 
Incorrect methods soon become habits and are very difficult to over- 
come. The position of the hand should not be shifted to draw the 
various strokes. 

Notes lettered entirely in capitals are not easy to read, for the reason 
that each word so lettered loses its characteristic word form by which 
it is recognized in reading ordinary printed matter. Capitals are now 
ordinarily used only where they would properly occur. In captions and 
titles it is frequently desirable to use all capitals, and in such cases a 
better appearance is obtained if the initial letters of the important 
words are made slightly higher than the others (Fig. 37). 

Compressed Lettering -Expanded 
■^ 



4^^ 



theJJse of Capitals in Titles 



Fig. 37. 

Inclined Small Letters.— In the construction of the small (or "lower- 
case") letters (Fig. 38) the stems of the tall letters are made the same 
height (five spaces) as the capitals, while the bodies of the letters are 
made three spaces high. The letter "t" is an exception, having a height 
of four spaces. The tail strokes of the letters "y," "j," "q>" "g" and 
"p" extend two spaces below the bases of the other letters, and in 
studying these letters an extra guide line should be drawn two spaces 
below the others. The location of the dot which forms a part of the 
"i" and the "j" should be noted. 

The letter "c" should be given very careful study for the reason that 
it is the important stroke in the construction of the seven letters follow- 
ing, the stroke being inverted in the case of "p" and "b." 

Vertical Capital Letters. — The construction of the vertical capitals 
(Fig. 39) is practically the same as that given for the inclined. It will 
be found advisable to tip all the letters slightly to the left rather than 
allow them to lean even slightly to the right. 

Vertical Small Letters. — While the vertical small letters (Fig. 40) 
are similar to the inclined in construction, it should be noted that the 
form used for the vertical "e" is not the same as that used for the 
inclined style. The style shown presents a better appearance with 
vertical lettering. The ellipses of the letters "o," "c," "e," etc., are 
tipped slightly to the left. 

Figures. — The finishing of an ordinary working drawing requires a 
greater use of figures than of letters. For this reason extra emphasis 



30 



should be placed on the study of the forms and construction of the 
figures (Figs. 41 and 42), which for the reason noted are made with 
as few strokes as possible. 



m 



& 



m 




n f-i h W=ssB = 



&= k? o </j—rnt 



S 



fiM-? 1 i'j & 




k 



mm 



& h i 



pE 



-f — t- 



wm 



si 



i i 



Fig-. 38. — Inclined single-stroke small letters. 



The Roman numerals present no difficulties, as they are merely combi- 
nations of the capita] letters "I," "V" and "X." They are, how- 
ever, made somewhat narrower in the present usage. The eross strokes 
on the upper and lower guide Lines are frequently made incorrectly. 



31 



The relative sizes and placing of letters, figures, fractions, inch marks, 
etc., are indicated in Fig-. 43. 



=T?- 



v*. J <^J 







m 



t= 



^ 



s::i 



\^/ nl^ 



« 



1 



N as 



X ^ y 



rgjr 






£ 



AA V V J Ul 



H^^^^f^i 



S 




HH 



1 



3 



5 





2/W 



Fig. 39. — Vertical single-stroke capital letters 



Modern Roman Capitals.— This style of lettering (Fig. 44) is much 
used in map work and in the construction of careful and elaborate titles 
on exhibition drawings. The height of these letters is shown divided 
into six equal spaces, and the widths stated in terms of these spaces. 



32 



The straight, heavy stems are given a width of one space while the 
shaded portions of the curves are made slightly wider. 




^^^^^^^@ 



M& 



3/4 




Be 



^^^^ 



^^=^^^^a 



^HP^^^^s 



±U ±_J 



m 



s5r~^3JtE: 



Fig. 40.— Vertical single-stroke s: 



mall letters. 



There are various exaggerations or corrections that arc riven the 
ProporJ '„: |"-''n T* '"'IT '" , 0, ' d, ' , • t,iat the * ™y "ee^operS 

S I,' ' ; - '•■ .'",:: '^.'.' ;." .I 1 ;; 1 - °™?v t •$, the r ,,n, „,, t 

r > ^> j > R and "B is placed slightly 



33 



more than three spaces above the bottom guide line. Also, the letters 
<<E/' "Z," "K," "X," "C," "G," "R," "B," and "S" are drawn 
narrower at the top than at the bottom. Unless these principles are 
observed the letters mentioned will look top-heavy. 




-tmtti/iniwi 



^^ 



feg 



Fig. 41. — Inclined figures. 



4^J- 



c' A A 4^ 



£ 



^— t=*T 



",)[) K )V 






I 



m 



m ( ) <t § (J 



\nn/i vi i vm § i 



i i 

Fig. 42. — Vertical figures. 

Another principle, common to the letters "J," "U," "0," "Q," 
"C," "G," "S" and the character "&," consists in extending the 
various curved outlines slightly over the top or bottom guide lines, as 
the case may be. If this correction is not applied these letters will not 
seem to be as high as the others. 



34 



The appearance of the letters "M," "A," "V" and "W" is improved 
if the sharp points common to these letters are extended a trifle beyond 
the extreme guide lines, and swung slightly away from the shaded side 
of the letter. 



.^ 



•^7^ 



-Slope Line 



7513^49225 lb, No.3l2-A 15% 
53?' 4li6 l82 L 0f Scale: /"= 100' 

Fig. 43. 

These letters are penciled in outline: only, the heavy stems not being 
filled in until the letters are inked. The steps to be followed in sketch- 
ing the letter "E" (Fig. 45a) illustrate the general procedure to be 
followed in drawing the straight-line letters. The correct form for the 
seriphs of the Modern Roman capitals is indicated in Fig. 45b. 

The curved letters are sketched by drawing the outside curved outline 
first. The inside of the curve is then drawn as a straight line, the 
thickness of each curve being made slightly more than one space at the 



ILTHFBZ 

II 1,11 ,i I \A => I I/ 1 I I 



I 3 



■>ilK— t<— Aj— ->i i<— -5a.— ->i !<- — 5— ~>\ ^—4^-—>\ (<-— 5— -i l<- — 5— -H 

NMHIM 



k— 4|— ->i K- — 6 h h*-— bj— ->i i<— - 5 * If- 



>\ k- 5?-— » 




K — 5i — »i l< — 5i — *i K™4j— ■*! k — 5i — *i j*-.--.-5--*i i«— -5—- * i* 6 »i 

Fig. II. Modern Roman capitals. 



35 



widest part. The steps to be followed in sketching the letter "0" ar* 
shown in Fig. 45c. In forming the curves of the letters "B" and "R," 
the thick parts are kept from running together by making the outside 
curves somewhat pointed in outline (Fig. 45d). 



m 



F 



5 



__j4 






1 



■a- 



■b- 



-< 





thus not thus 



-c- -d- 

Fig. 45. — Construction of Modern Roman capitals. 

The horizontal distances between the letters of a word should vary with 
the different letter combinations, the clear spaces included by the out- 
lines of adjacent letters being kept approximately uniform in area. 

In inking these letters one should, proceed as in the pencil work. 
When the outlines are inked, all pencil marks are removed with a soft 
eraser. The wide stems of the letters are then filled in with a coarse 
writing pen or a ruling pen with the nibs nearly closed. 



abcdefghijklmn 
opqrstuvwxyz 



Modem Roman 



abcdefghijklmni 
opqrstuvwxyz i 



Stump Letters 



Fig. 46. 



Roman Small Letters. — The small letters of the modern Roman 
alphabet (Fig. 46), together with the capitals (Fig. 44), may also be 



36 



ii i , I i i i .1 1/ i/i \ 



->ili<— k— 5^— * t<— ■ 6 * i<-'-- -6- 




k— 5|— ->i cc— 5~— » 'k— -6— -->i 



NMAVWM 

re— -6— ~>i N k-— -7 ->t i< 7— — >1 k— -fi— ->i i< 9 >i k— -6— -H 



*YJUO 





k— -6£ >t I* 6 H k— -5;— -->! k— -5f— ->i k— -5|-->l i<— 5|— ->i k— -6|— -- >i 



Fig. 47. — Block capitals. 

drawn in the inclined or italic style, the forms of the letters otherwise 
remaining unchanged. 

Stump Letters. — Stump letters (Fig. 46), a modified style of small 
italics, are often used with the italic Modern Roman capitals on maps 
and patent-office drawings. The heavy strokes of these letters, except 
in the case of very small letters, are first outlined and then filled in. 
While the hair lines may be made as part of the body stroke, it is 
generally advisable to form these with short down-strokes to the left. 
This avoids the tendency of the pen to catch, and. also prevents dragging 
ink over the angles of the letters. 

Block Letters. — The construction of the block capitals (Fig. 47), 
sometimes termed the Commercial Gothic alphabet, calls for some of the 
corrections applied in the construction of the Modern Roman alphabet. 
The cross-bars of the "H," "F," "E," "P," "R" and "B" are placed 
slightly above the middle height, while the letters "J," "U," "0," 
"Q," "C," "G," "S" and "&" all extend slightly beyond the limiting 
guide lines. 

Block letters are penciled in outline and filled in solid when inked. 
All stems are made one space wide. A slight pointing of the sharp 
corners improves the appearance of these letters. 



37 

I DP 



D 



(a) 



^ 






^■'V^'Reservoir open for cleaning 

(b) 



Fig. 48. — Block lettering pens. 



ABCDE 
FGHIJIC 
LMNOP 
Qj^STU 
VWXYZ 



Fig. 49.— Old Roman capitals. 



38 

The spacing of block letters should ordinarily be snch that the area 
included by outlines of adjacent letters is about equal to one-third' of 
the area used by the letter "M." 

Single-Stroke Block Letters. — Heavy block letters may be drawn 
rapidly with single strokes made with special block-lettering pens (Fig. 
48), or with special steel pen-points made with broad flattened points. 

Old Roman Capitals. — The Old Roman letters form the basis of prac- 
tically all of the lettering used in architectural drafting, and although 
rather difficult of execution they should be given careful study by any- 
one training for this class of work. In the Rennaissance alphabet 
(Fig. 49) the letters are made nine spaces high, with the light and 
heavy stems one-half a space and one space wide, respectively. 



ABCDEFGHUKLMNO 
PQRSTUVWXYZ 

ab c def gKvj klmno p 
qr^tuvwxyz. ■ 

ABCDEFGl-iy KLMNO 
PQRSTUVWXYZ 



Fig. 50. — Single-stroke Roman. 

In classical inscriptions, the letter "I" is customarily substituted for 
"J," and "V" for the letter "U," due to the fact that the letters "J" 
and "U" are comparatively modern additions to the alphabet. 

The Old Roman letters are open to many modifications of form, which 
if made with due regard to proportions and composition give results 
that are varied and pleasing. 

Single-Stroke Roman. — The single-stroke style shown in Fig. 50 (a 
and b) is derived from the Old Roman alphabet and retains much of its 
beauty and individuality. These simple letters may be formed rapidly 
and are much used by architects on working drawings. A modified 
style is indicated in Fig. 50c. 



39 

Orthographic Projection 

If an object is viewed through a transparent plane (picture plane) 
and its outlines traced on the plane as seen, a perspective projection or 
drawing of the object will result (Fig. 51a). The size and shape of the 
outline thus projected will depend on the relative positions of the ob- 
server, the picture plane and the object. As all the rays or lines of 
sight from the object to the eye converge in one point (the point of 
sight), it is aparent that no line on the object will show or project in 
its true length unless it is actually in the picture plane. All lines be- 



Object- 



Picfure Plane -"] 



Project. 



Projecting Lines 
Point of Sight 



-^y 



Object-- 
Picture Plane -sS 











/ 1 

Projecting" ' 
Lines\\ 




^' - 


4r * 


-\ 


/ 
/ 





' > ~ Projection 



(a) 



(b) 



Fig. 51. — Perspective projection (a) and orthographic projection (b) compared. 

hind the picture plane will be projected shorter than they are. This 
foreshortening of the lines of an object makes such a projection unsuit- 
able for use as a working drawing, chiefly because the lines cannot read- 
ilv be measured or dimensioned. 




Projecting! 
lines -^ 





1 




1 ' 




1 




. / 




, 




1 






, 




























/ 


1 1 


1 1 


/ 


1 


1 




1 , 


1 






i 




1 


1 




1 






1 






1 


1 


1 


r 




i 




1 

1 


1 

1 


1 


1 

1 


/ 


/ 


1 


' 


1 


1 


1 

1 


1 


i 








h 























s - Projected Outline "--'Picture Plane 

Fig. 52. — Dissimilar objects giving identical projections. 

Orthographic Projection. — If the observer is considered as having 
moved an infinite distance away from the plane and the object, the lines 
of sight (projecting lines) locating the outline will become parallel 



40 



(Fig. 51b,) and every line parallel to the picture plane will project in its 
true length. 



Transparent 

Box - 



(a) 



^ 
























\ 

\ 
V 






i 


i — - — — 




1 

J 

1 
1 




Si 










Top 


















1 

1 

1 






i 
i 














1 










1 
1 
1 




J 


-- 


s^- 






u 


LFT En 


D. 


s 
/ 
<* 


Front 




<s- 


'IGHT E 


ND 


4 

-> 

Transparent ' 
Box Opened v 














l_ 






c * 




(b) 






Bottom 







Fig. 53. — Theory of orthographic projection. 



When projecting- lines are parallel to each other, and also perpen- 
dicular to the picture plane, the projection or view obtained is an ortho- 
graphic projection. Working drawings are made up of two or more 
such projections. The object is usually placed with one face parallel 
to the picture plane so that all lines on this face will project in their true 



41 



length and relative positions. A second view is necessary to show the 
dimension of the object perpendicular to the picture plane (the plane 
of the drawing). Frequently a second view is necessary to define the 
shape of the object, as in the case of each of the objects shown in Fig. 52. 
These objects project as rectangles, identical in each case. 

Arrangement of Views. — To get an understanding of the principles 
underlying the making and arrangement of additional views, consider 
the object to be inside of a rectangular box (Fig. 53a) having transparent 
sides, each of which may be taken as a picture plane for an orthographic 
projection or view. The object is so placed that its various faces are 
parallel to the sides of the box, so that the projections or views will 
project their true shape and size. The projections of invisible edges 
are always shown as dash lines. 

The sides of the box are then opened out by swinging them away from 
the object, this giving the arrangement of the views indicated in 
Fig. 53b. In making the actual working drawings (Fig. lb) the lines 
representing the edges of the imaginary box are omitted and only the 
necessary views (usually two or three) are drawn. 



(fwjf ) fflf 



n 



\J^_ 



^~~ 


T" 

1 
1 
. L — 

"'La 


/-m 





Fig. 54. — Orthographic projections. 



Two groups of simple objects, together with their representations in 
orthographic projection, are shown for study in Figs. 54 and 55. The 
student should practice making freehand sketches of simple objects 
showing two or three views properly arranged. 

Auxiliary Views. — Where a face of an object is not parallel to the 
picture plane on Avhich it is projected, the resulting projection or view 
will be foreshortened or distorted. 

In order to avoid this difficulty resort may be had to an auxiliary 
view. Such a view is a projection made on an imaginary picture plane 
taken parallel to the face to be projected. This is illustrated in Fig. 
56 (a and b). In Fig. 56c the whole piece is shown in the auxiliary view, 
but where the piece is more complicated this view need only show the 
details of the inclined face. 

Sectional Views. — Frequently the construction of an object may be 
shown more clearly if a portion of it is considered as having been cut 
away so as to show the interior. The cut is assumed to be made by an 
imaginary plane (57a) and the drawing so made as to represent the 



42 

object as though it were so cut and the near or front portion removed. 
Thus the lower view in Fig. 57c is drawn to represent the object with 
the front portion cut away as in (b). The solid portions so cut are usu- 
ally indicated by cross-section lines which may be varied to indicate in 
a conventional manner the various materials used (Fig. 58). The con- 
ventional method of designating a section and indicating just where it 
is taken is shown in Fig. 57c. 





£^ 





H 



~ISI 



Fig. 55 

Where a piece is symmetrical it is often convenient to show one-half 
in section (Fig. 59) and the other an outside view. Such a view is called 
a " half -section. " 

Revolved sections are frequently cut into ordinary views, as indicated 
in the detail drawing of the plug wrench (Fig. 60). 

The conventional breaks shown in Fig. 61 are used in a manner simi- 
lar to the revolved sections, and particularly when a piece witli a uni- 
form cross-section is too long to be shown to scale. 

Intersections. — Most objects may be thought of as being made up of 
parts of various solids (such as spheres, cones, cylinders and prisms) 
joined together. The surfaces of any two of such solids intersect in what 



43 



uxi/iary picture p/ane 
parallel to oblique 
face of the object 



Transparent Box 




Fig. 56. — Auxiliary projections. 



K 



XV 



i^^g a 



v 



—Cutting Plane 



(a) 



1/ 



?Hjecf (b) 

' (Front portion removed) 



Fig. 57. — Sectional views. 



7 



; • 




1 



Section A- A 

(c) 



44 







WROUGHT IROI* 



COMP.OR BRASS 




LEAD OR BABBI 





VULCANITE WOOD 

Fig. 58. — Cross hatching symbols. 



mm. 



77777, 



^tttM 




Fig. 59.— A half-section. 




Plug Wrench 

Fig. 60. — A detail drawing. 



45 

is termed a line of intersection, such a line being common to both sur- 
faces. 

In representing an object by orthographic views it is frequently neces- 
sary to obtain the projection of such lines of intersection. In general 
this can be done by so passing a series of imaginary planes through both 
surfaces that each plane will cut straight lines or circles from each. 



s^^l LJ L>^ Ld 



i^O 



Square Round Pipes Rolled Shapes 

Fig. 61. — Conventional breaks. 

These lines lying in the cutting plane will intersect in points common 
to both surfaces. A series of such points connected up will locate the 
line of- intersection of the two surfaces. 



ic" Cutting Plane 




Cutting Plane - - s 



Line (s") cut from surface 
of triangular prism - - 





Line (s'J cut from surface 
of square prism 



point on required 
line of intersection 
(common to both surfaces) 

-Required line 

of intersection 



Fig. 62.— Method of finding points on the line of intersection of two surfaces. 



The application of this method to finding the line of intersection of 
two prisms is illustrated in Fig. 62c. The cutting plane shown cuts a 
vertical line from the surface of the square prism, and a horizontal line 
from the surface of the triangular prism. These two lines intersect in a 
point which is common to the surfaces of both prisms and hence a point 
on the required line of intersection. The solution is shown pictorially 
in (a) and (b). 

Two methods of finding the line of intersection of the surfaces of two 



46 



cylinders are similarly illustrated in Fig. 63, while Fig. 64 shows similar 
methods applied to the intersection of a cylinder and a cone. The inter- 
sections of any of the numerous combinations of surfaces can be found 
by the application of this method. 




Fig. 63. — Two methods of finding points on the line of intersection of two cylinders. 




(b) (c) (e) (f) 

Fig. 64. Two methods of finding points on the line of intersection of a cone and a cylinder. 



Working Drawings 

A complete working drawing carries all the dimensions and other in- 
formation that the workman needs in forming or finishing the piece or 
structure. It should not be necessary for the workman to take any 
dimensions from the drawing by scaling, or to do any computing to ob- 
tain them. 

A working drawing of a separate part of any machine or structure 
is called a detail drawing (Figs, lb and 60). A drawing which shows 
the various parts of a machine or structure in their assembled posi- 
tions is called an assembly or an assembled drawing (Fig. 65). Such 
drawings have various uses and are characterized by a lack of detail 



47 



dimensions — only the over-all and other important dimensions (such as 
to center lines) ordinarily appearing. 



Conventional Lines. — If all 

the lines used on a working- 
drawing were drawn exactly 
alike, the drawing would not be 
easy to read. For this reason 
the lines used are varied in ap- 
pearance so that they may be 
recognized readily. This may 
be done by varying the weight 
of the lines or by breaking them 
into various combinations of 
long and short dashes. The con- 
ventional lines shown in Fig. 66 
are those commonly used on 
engineering drawings. Center 
lines should be penciled as 
continuous lines, these being 
changed to the conventional dot 
and dash line when inked or 
traced. 




Fig. 65. — An assembled drawing. 




Border line - Heavy full line (32" to fa) 
Visible Outline -Medium full line (^g 'fog,' ') 
Hidden Outline -Medium dash line. 
Center line - Thin dot and dash line (j&toJh) 
Extension line - Thin long dashes. 
Dimension line - Thin full line- 



•l^* s-Solid head- convenient to make with 
^— ' bail-pointed pens. 



Cross-hatching line - Thin full line 
Auxiliary line - Thin dash and dots line 
Architectural bneak line - Thin line 



Break lines -Medium irregular lines 
Conventional lines. 



Order of Inking. — A systematic and logical procedure in inking 
drawings will result in a saving of time and better results. 



48 



In general, it is best to proceed in about the following order : center 
lines, small circles and circular arcs, large circles and circular arcs, ir- 
regular curved lines, straight horizontal lines, straight vertical lines, 
hidden circles and arcs, hidden straight lines, dimension lines, dimen 
sions, notes, section lines, the title and the border lines. 

Tracing cloth shrinks and expands to such an extent (due to atmos- 
pheric changes) that it is a good plan when tracing a large drawing to 
finish one view at a time or to work on only such a portion of the draw- 
ing as can be finished the same day. This plan largely avoids the 
difficulty of getting the various lines previously inked to agree with 
the drawing. 



Visible Outlines -^ 



, - - ^Spaces 



v "-*» 






i 

4- 


t 


'T-- 


, Inch Marks 










if i 








V 


Dimension 




C\ 


? /// 






~F 


Lines ' 


" x 


\ 


3 2 






^~^~~ Lines 






-£-r- 


^ Apnow 
■~ Heads 




l 
1 
1 

L-N 




1 
1 
1 

[ 1 





Hidden Outlines 



Fig. 67. — Use of conventional lines. 



Dimensioning. — Dimensions are indicated on working drawings by 
means of figures placed in line with and between double arrows (Fig. 
66f), the points of which touch the outlines or extension lines limiting 
the measurement (Fig. 67). Sometimes dimension lines are inked in red 
with figures and arrowheads (Fig. 66g) in black, but the use of colored 
inks is neither general nor recommended. Extension lines (Figs. 66e 
and 67) may be full lines or dash lines. Dimension lines are usually 
broken for the insertion of the figures except in structural steel drafting, 
where it is customary to place the figures above the dimension lines. 

The figures indicating feet and inches should be separated by a dash 
in every case, thus, V — 4 1 /*/'. If written 1'4%" the dimension is apt to 
be read as 14Vfc". Dimensions of even feet are indicated thus, 6' — 0". 
In some classes of work drawings are dimensioned entirely in inches, 
and in such cases the inch-marks are frequently omitted. 



49 

Various methods and devices of use in arranging and indicating' dimen- 
sions are shown in Fig. 68. The satisfactory placing of the figures de- 
pends on the space available and the ingenuity of the draftsman. No 
system of arranging dimensions is applicable to all conditions. Every 
effort should be made to place on the drawing in an orderly arrange- 
ment just the dimensions that will be needed in forming the piece. 



^ Not thus «i 3" 

Nor thus i I 



M^M^'MMM" 




A 
& 




Thus 



Thus On thus \^2^'h\ \*r2%r^ Thus 
Thus Not thus 




U 

Not thus Thus 

Fig. 68. — Arrangement of dimensions 



Not thus 




Not thus 



Some knowledge of the shop methods to be used is therefore necessary in 
order to dimension a piece properly. It is well for the draftsman to 
imagine himself about to construct the piece, and then mentally to trace 
through the various operations necessary to produce it. Then he is in 
the proper frame of mind to supply the necessary information in the 
clearest and most convenient manner. 

The view which most clearly defines the piece should be selected and 
dimensioned first. The more important dimensions should be indicated 
first, all similar dimensions being put on at the same time. Flat pieces 
should be dimensioned by placing all the dimensions but the thickness 
on the outline view. 

A careful study of Fig. 68 and the various dimensioned drawings 
shown in this publication will familarize the student with good practice 



50 



The following suggestions should always be kept in 

These may be secured by 



in dimensioning, 
mind: 

1. Clearness and legibility are essential, 
neatness in arrangement and care in forming arrowheads and 
figures, and by avoiding any crowding of dimensions. 

2. Dimensions should not be repeated on different views without some 
special reason. 

3. Finished surfaces should be located from other finished surfaces or 
from center-lines. 

4. Dimensions should be placed so that they may be read from the 
bottom or the right-hand edge of the drawing (Fig. 68). 

5. All notes should read from the bottom edge. 

Standard Details. — Such small details as have been standardized do 
not require complete dimensioning. This may apply to such details as 
screws, tapers, piping, wire, sheet-metal, rope, chain, pins and rolled 
steel sections. 

Finish. — Where any chance for confusion exists as to the surface 
finish to be given to any part, the finish should be carefully indicated 
by means of a note and an arrow leading to the surface referred to. 

The usual finish indications are as follows: Rough, Rough-Turned, 
Ground, Polished, Cored, Drilled, Reamed, Loose Fit, Scraped, Chipped 
and Spot-Faced. 

The letter "f" is frequently used as an abbreviation of the word 
"Finish." The manner of its use is indicated in Fig. lb. 

Notes.' — Explanatory notes should be added to a drawing whenever 
the drawing can be made clearer by their presence. Frequently a care- 
fully worded note saves time by making the drawing of another view 
unnecessary. Brevity of wording is desirable so long as the exact mean- 
ing is clearly stated. 





No. 


Name of Part 


No.Req'd, 


Material 


Remarks 


Dr. No. 




2485-1 


Upper Shear 


1 


Too/ 5 feel 


Harden & Grind 


2485 




2485-2 


Upper Stripper 


I 


„ 


n 


2485 




2485-3 


Lower Shear 


'2 


,- u 


„ 


2485 




2485-4 


Lower Str/pp&r 


2 


,, 


« 


2485 




2486-/ 


Upper Stripper Spring 


1 


Spring St. 




2486 































Fig. 69. — A bill of material. 

Bills of Material. — Working drawings frequently carry a tabulated 
form known as a "bill of material" which states the names and the 
number of each of the various pieces needed to make up one complete 
machine or structure. The items of information included vary consider- 
ably, but the form shown in Fig. 69 may be taken as typical. 



51 

Title. — Every drawing should carry a title of some sort. In its 
simplest form a title should contain the title proper, the name of the 
draftsman and the date. Titles may be open or boxed, both styles being 
illustrated in Fig. 70. Titles on engineering drawings should be simple 
in style and arrangement. 



















ON. 1 TO. 


SCALE 








CHAMStD 


OR 


1 












TR 


MATERIAL 








THE PIERCE-ARROW 
MOTOR CAR CO. 
BUFFALO, N.Y. 






CM 





















CIoms 




Sheet 












Date 












ASSOCIATED MANUFACTURERS CO. 







































































DATE 


MARK 


CHANCE RECORD 


out. 




CAUTION 

DECIMAL DIMENSIONS MUST 
BE MAINTAINED. 

.010 EACH WAV CAN BE ALLOW- 
ED ON DIMENSIONS NOT OTHER- fl 
WISE SPECIFIED. 





Cadillac Motor Car Co. 



DETROIT. MICH. 

DRAFTING ORDER NO. 



TOOL SHEET 
C 



Fig. 70. — Various title forms. 



Some concerns having many drawings save expense and secure greater 
uniformity and better appearance by printing the titles on their trac- 
ings with type. Sometimes only the standard portion of the title is 
printed, the variable portion being added free-hand by the draftsman. 

Screw Threads. — The sharp edge of a screw thread is a curve known 
as a helix (Fig. 71q), and its projection on a plane parallel to its center- 
line is a curved line. Ordinarily straight lines are substituted for these 
curves, the ordinary V-thread being drawn as in Fig. 71a. 

As the drawing of individual threads takes too much time, threads 
are usually indicated on working drawings by some one of the various 
conventional methods shown in Fig. 71. Where the lines representing 
the edges of threads are drawn perpendicular to the center-line, the 
thread is assumed to be right-hand unless otherwise specified. 



52 

Bolts and Nuts. — In Fig. 72 are shown the dimensions and the con- 
ventional methods of drawing U. S. standard bolts and nuts. 




Fig. 71. — Conventional representation of threads. 




Bolt 

Diam. 
D 


Thcls 
per 
Inch 


Root 
Diam. 


Short 

Diam. 

A 


Long 


Diam. 


Thickness 


Bolt 

Diam. 

D 


Thcls. 
per 
Inch 


Root 

Diam. 


Short 

Diam. 

A 


long Diam. 


Thickness 


c 

jojuare 
B 


Hex. 
C 


Hut 
D 


Head 
E 


Scjuare 
B 


Hex. 

C 


Nut 
D 


Head 
E 


4 


to 


diss 


l 


0.707 


0.578 


/ 
4 


/ 
4 


# 


G 


1.283 


$ 


3.358 


2.743 


¥ 


'i 


/6 


18 


0.240 


19 
32,, 


0.840 


0.686 


16 


19 

64 


1 


% 


7.389 


4 


3.623 


2.960 


// 


4 


3 
8 


16 


0.294 


1! 
16 ■ 


0.972 


0.794 


3 
8 


// 


'i 


5 


7.490 


?+ 
u 


3.889 


3.176 


# 


// 


7 
16 


14 


0.345 


25 

32 


1.105 


0.902 


7 


25 

64 


// 


5 


1.615 


4 


4.154 


3.393 


// 


/£ 


/ 
2 


13 


0.400 


7 

8 


1.237 


1.0 II 


1 


7 
16 


2 


4 


1.711 


it 


4.419 


3.609 


2 


a 


iS 


It 


0.454 


3/ 
32 


1.370 


1.119 


9 


31 
64 


H 


4 


1.961 


H 


4.949 


4.043 


H 


>i 


s 

8 


II 


0.507 


4 


1.502 


1.227 


4 

8 


17 
32 


?£ 


4 


2.175 


4 


5.479 


4.476 


H 


<ie> 


3 
4 k 


10 


0.620 


4 


1.768 


1.444 


3 
4 


5 
8 


4 


4 


2.425 


4 


6.010 


4.909 


1 


£ 6 


7 
8 


9 


0.731 


4 


7.03S 


1.660 


7 
8 


23 
32 


3 


3$ 


2.629 


4 


6.540 


5.342 


3 




7 


8 


0.838 


4 


2.298 


1.877 


1 


13 
16 


4 


4 


2.879 


5 


7.070 


5.775 


H 


% 


// 


7 


0.939 


HI 


2.563 


2.093 


¥ 


29 
32 


4 


3 4 


3.100 


H 


7.600 


6.208 


4 




i 


7 


1.064 


2 


2.828 


2.310 


i 


1 


$ 


3 


3.317 


% 


8.131 


6.641 


4 


$ 


ji 


6 


1.158 




3.093 


2.527 


'i 


4 


4 


3 


1567 


4 


8.661 


7.074 


4 


4 



Fig. 72.— Dimensions of U. S. standard bolts and nuts. 



53 

Cap Screws.— The method of drawing the various styles of cap 
screws, together with a table of dimensions, is shown in Fig. 73. It 
should be noted that the heads are of smaller diameter and thicker than 
those of standard bolts. 




Cs^ 



-F- 

70 l 



y> 



k-/?-> 



K-/7-H 



I I 

K-Z?->' 



I I I I 

k-D->\ K-D->\ 



D 


A 


3 


c 


E 


F 


G 


D 


A 


3 


C 


E 


F 


6 


D 


A 


s 


C 


1 






3 
16 


7 
3? 


i 
4 


3 
32 


7 
16 


8 


9 
16 


5 
8 


3 

4 


13 

16 


17 
64 


7 
8 


*i 


's 


'i 


3 
16 






1 
4 


16 


3 
8 


9 
64 


1 
2 


3 
4 


8 


3 
4 


13 
16 


7 

8 


17 

64 


1 


// 


4 


% 


1 

4 


7 
lf> 


3 
8 


3 
8 


16 


15 


5 
12 


9 

16 


13 
16 


II 
16 


13 
16 


IS 
16 


I 


3 
16 


i 


// 


4 




5 

16 


I 


16 


7 
16 


9 
16 


5 
8 


Tz 


5 
8 


7 
8 


4 


1 
8 


J 


i 


33 

64 


>i 


'i 


// 




3 

8 


9 

16 


1 
2 


9 
16 


1 
8 


3 
4 


17 
64 


3 
4 


I 


7 
8 


1 


•i 


<§ 


7 
16 











Fig. 73. — Dimensions of cap screws. 







\F^\\ ^ 






K- -£- -» 

:bgj: 



Flat Head Round Head Flat F/Ih'sfer Head Ova/ Fi/ listen Head 



Ho. 


J;j~. 


Thds, 


A 


3 


c 


D 


E 


F 


6 


No. 


Diam, 


Thds. 


A 


3 


C 


D 


E 


F 


19 





,060 


80 


.113 


.030 


.106 


.043 


.0894 


.01/6 


.0496 


13 


,216 


28 


.424 


,120 


w 


W 


.3452 


1405 


.1868 


. 


.013 


13 


,m 


.011 


.110 


.011 


.1101 


,04bl 


.0600 


14 


,242 


24 


.476 


.IK 


441 


.I6« 


■3879 


,151/ 


, 


.08b 


U 


.ltd 


.045 


.114 


.ObO 


.1130 


.0148 


.0/31 


16 


.268 


22 


.128 


.110 


491 


m 


.4305 


1748 


.2321 
.2554 
.2782 
3011 


i 


,049 


56 


MO 


.013 


.1/8 


.W 


.1130 


.0631 


.0818 


18 


.294 


20 


.580 


.164 


.119 


206 


.473/ 


,1930 


4 


.113 


46 


.316 


.ObO 


,303 


.018 


.1/41 


.0/19 


.0913 


30 


.320 


20 


.612 


.179 


.187 


??4 


.5/58 


.3098 


i> 


.I3t> 


.44 


.343 


Ml 


.336 


.081 


.I960 


.0801 


.1068 


23 


.346 


18 


.684 


.194 


,W 


?4? 


■5584 


2262 


o 


,hb 


40 


■368 


.011 


.310 


,091 


.31/0 


.0890 


.1180 


34 


,272 


W 


.736 


.209 


.681 


?fiO 


.60/0 


2435 


.3240 
.3469 
.3698 


/ 


.bi 


16 


.344 


.083 


.314 


.106 


.3186 


.0916 


.1396 


36 


.398 


16 


.788 


.??4 


.711 


?7Q 


.643/ 


2606 





.164 


i6 


330 


.030 


.398 


,111 


.3199 


.1062 


.1410 


IS 


.424 


14 


.840 


.219 


.774 


.20/ 


.6863 


.2778 


f 


.III 


33 


.346 


.041 


,133 


.134 


.38/3 


.1/48 


.534 


30 


.410 


14 


.892 


.214 


,877 


.3/1 


7?an 


.2950 


3927 


10 


.190 


10 


.3/3 


.101 


.146 


.111 


.3036 


.1314 


.1639 














.... 





Fig. 74. — Dimensions of machine screws. 

Machine Screws. — The proportions of the various sizes and styles of 
machine screws are shown in Fig. 74. Machine screws are specified by 
gage numbers as indicated. 



54 



K -/?--> 




Square Head 
(Round Point) 




Cone Point 



\k-D-*\ 




Low Head 
(Hat Point) 




Headless 





Socket Head 
(Cup Point) 




Hanger Point Flat Pivot Point Round Pivot Point 
Fig. 75. — Dimensions of set screws. 



Perfect Threads P\ 

*■ Taper jj, "per Inch 




|<- - -4 Th'ds - - ->^?7h'd&\<- - - 



0.8xQut.Diam.-t-4.8 
No. of Th'ds per Inch 



Diameters 


Th'ds 
per 
Inch 


Internal 
Area 


Distance 

Pipe 

Enters 

C 


Diameters 


Th'ds 
per 

Inch 


Internal 
Area 


Distance 

Pipe 

Enters 

C 


Hominal 
Inside 


Actual 

Inside 

A 


Actual 

Outside 

B 


Hominal 
Inside 


Actual 

Inside 

A 


Actual 

Outside 

3 


t 
8 


0.210 


0.405 


27 


0.051 


0.19 


5 


3.067 


3.500 


8 


7.383 


0.95 


l 
4 


0.364 


0.540 


18 


0.104 


0.29 


4 


3.548 


4.000 


8 


9.887 


1.00 


3 
8 


0.494 


0.675 


18 


0.191 


0.30 


4 


4.026 


4.500 


8 


12.730 


1.05 


1 


0.623 


0.840 


14 


0.304 


0.39 


4 


4.508 


5.000 


8 


15.961 


1.10 


3 
4 


0.324 


1.050 


14 


0.533 


0.40 


5 


5.045 


5.563 


8 


19.986 


7.16 


I 


1.048 


1.315 


Hi 


0.861 


0.51 


6 


6.065 


6.625 


8 


28.890 


1.26 


i 


1.380 


1.660 


nt 


1.496 


0.54 


7 


7.023 


7.625 


8 


38.738 


1.36 


it 


WO 


1.900 


tt 


2.036 


0.55 


8 


7.982 


8.625 


8 


50.027 


1.46 


z 


2.067 


2.375 


Hi 


3.356 


0.58 


9 


8.937 


9.625 


8 


62.720 


1.57 


4 


2.468 


2.875 


8 


4.780 


0.89 


10 


10.019 


10.750 


$ 


78.823 


7.68 



Fig. 76.— Dimensions of standard steel and wrought-iron pipe. 



55 

Set Screws. — In Fig. 75 are shown the various styles and propor- 
tions of set screws used in machine work. Other combinations of the 
various heads and points shown may be used. 

Standard Pipe. — The threads on U. S. standard steel and wrought- 
iron pipe differ from the standard V-thread as indicated in detail in 
Fig. 76. The various dimensions of value to the draftsman are stated in 
tabular form. 

Decimal Equivalents of Fractions of an Inch 



5 

32 "i 

64 



11 

j 64 

32 "ii 

B4~ 



-.0/5625 
-03/25 
-.046875 
-.0625 



-,078/25 

-09375 

-109375 

t/25 



■ .140625 
-.15625 
-.771875 
-.1875 



-.703/25 
-.21875 
-.234375 
-.25 



64' 



-.265625 
-.28/25 
-.296875 
-.3/25 

-.328/25 
-.34375 
-.359375 
-.375 



- -.390625 

- -.40625 
--.42/875 

- -.4375 



-.453125 
-.46875 
-.484375 

■-.5 



76 



.575625 
.53725 
.546875 
-.5625 

-.578/25 
-.59375 
-.609375 
.625 

-.640625 
-.65625 

.67/875 
-.6875 

: 703/25 
-.71875 
.734375 
t75 



94 



63. 



-i765625 
--.78725 

- -. 796875 
--.8/25 

- 7828/25 
--.84375 
--.859375 
-7875 



-.890625 
-.90625 
-.92/875 
y9375 



■ -.953725 
-.96875 

■ -.984375 
7.0 



Fig. 77. 

Decimal Equivalents. — A table of decimal equivalents of the various 
fractional parts of an inch is inserted (Fig. 77) for the convenience of 
the student. The decimal equivalents for each sixteenth of an inch 
should be memorized. 



Reproduction of Drawings 

The tracings which the draftsman makes from his drawings are not 
suitable for shop use. They are permanent records and are seldom 
allowed to leave the drafting room, as they would be damaged and per- 
haps lost if sent to the shops. The necessarj^ reproductions of the trac- 
ings that are needed in the shop and elsewhere may be made in various 
ways. 

Blueprinting. — The cheapest process and the one in common use is 
called "blueprinting," this being simply a photo-printing process by 
which any number of copies can be made from one tracing. Tracings 
made on tracing cloth or tracing paper with a soft pencil can be blue- 



56 

printed, but better results are secured from tracings inked in the usual 
manner. 

Blueprints are made on white paper or cloth which has one side coated 
with a chemical sensitive to light. When fresh the sensitized side is of a 
pale yellowish-green color which with age, or on exposure to the light, 
turns a greyish-blue. If an unexposed piece of fresh paper is washed 
this coating is removed, leaving only the white paper; while a piece 
properly exposed to the light will turn a deep blue when similarly 
treated. In blueprinting a tracing, the opaque ink lines protect the coat- 
ing underneath from the action of the light while the background is 
being exposed. 

In making a blueprint the inked side of the tracing is placed against 
the glass of the printing frame (Fig. 78) and the sensitized side of the 



Hinged Back ■» 




, Felt Pad 

Blue Print 
Paper 



- Glass 
Tracing 



Fig. 78. — A printing frame. 

blueprint paper against the tracing. The back of the printing frame 
is then locked in position to hold the tracing and the paper firmly in 
contact, and the glass side of the frame exposed to sunlight from one- 
half minute to several minutes, depending- on the light and the speed or 
sensitiveness of the paper. The paper is then removed from the frame 
and washed in clear water for several minutes to fix the blue back 
ground and to wash the lines to a clear white. Prints hurriedly washed 
will fade badly on exposure to strong light. Prints may then be hung 
up to dry, or may first be dipped in a weak sodium bichromate solution. 
This operation improves the color and clearness of the prints and should 
be followed by a rinsing in clear water. The prints should be hung with 
the lower edge at an angle with the horizontal, so that the water will 
drain off at the lowest corner. Wet prints should be kept out of strong 
light and. where the air can circulate freely. Drying can be materially 
hastened if the excess moisture is removed from the print by means of a 
rubber squeegee such as is used in window washing. 

It should be noted that this process, photographically speaking, pro- 
duces a negative in that the black lines of the tracing are changed to 
white lines on a dark (blue) background. Changes on blueprints may 
be made by the use of white and bine pencils, or the bine of the back- 



57 

ground can be bleached white by using an alkaline solution in the pen — 
such as washing soda with a little gum arabic added to prevent spreading. 
The practice of changing blueprints is not one to be recommended, as it 
is better to make any desired changes on the tracing and then to make 
new prints carrying a new date to indicate that a revision has been 
made. 

Slow-printing paper keeps better and makes better prints than the 
rapid papers. Fresh paper prints more slowly than old but washes more 
quickly and will give whiter lines. 

A good blueprint can be made from typewritten copy made on thin 
paper with black carbon-paper placed both in front and behind. Inked 
drawings on thick paper may be printed readily if transparentized with 
oil, hot paraffin, or, temporarily, with benzine. 

Where much blueprinting is done, electric printing machines are con- 
venient and make the process independent of weather conditions. These 
machines may be had in many forms, varying from those printing 
separate sheets to those which print on continuous rolls of paper and 
automatically wash, "potash/ 7 dry, iron and reroll the paper u Every 
large city has its printing concerns, and it is more economical for firms 
requiring only a moderate amount of blueprinting to patronize these 
establishments than to maintain their own printing plant. 

Blue-line and Brown- line Prints. — Blueprint "positives" may be 
made by first printing a negative on thin Van Dyke paper or cloth 
which gives white lines on a dark-brown and opaque background. This 
negative is printed and washed in the same manner as an ordinary blue- 
print. It is then placed in a "hypo" or fixing bath for a moment, this 
being followed by a rinsing in water before the negative is dried. The 
blueprint positive, or "blue-line" print, is made by blueprinting in the 
usual manner, using the Van Dyke negative instead of a tracing. If de- 
sired the positive may be printed on Van Dyke paper, this process giving 
dark-brown lines on a white ground. Such prints are considerably more 
expensive than blueprints, but ha\ T e important advantages in some cases. 

Direct Positive Prints. — Certain printing papers may be obtained 
which produce blue-line or black-line positives with one printing. While 
these papers are relatively expensive, slow printing and frequently of 
poor keeping qualities, their use is a decided convenience under certain 
conditions. Most of these papers require no special developing solutions, 
being handled like blueprint paper. 

Photography. — Tracings are frequently photographed, usually to a 
reduced size, and photographic prints made from the negatives. Such 
photographic reproductions of large drawings are a decided convenience 
to men in the field on account of the reduction in size of the sheets. This 
process, however, is relatively expensive. 

Direct Photography. — Copies of drawings, blueprints, etc., may be 
made by means of a special type of camera containing a prism so placed 
as to prevent the usual reversal of image in the negative. The negative 
is used as the reproduction, with the usual color reversal of light and 



58 

dark. A blueprint, when thus reproduced, has dark lines on a light 
background. The Photostat, Rectigraph and Cameragraph are the trade 
names of machines making use of this principle. 

Gelatine Process. — Drawings may be reproduced on tracing cloth or 
on paper by a special process in which a special "matrix" print is first 
made on a blueprint machine and then transferred to a flat gelatine sur- 
face. The impression is then inked,, and the copies or prints rubbed into 
contact andj pulled from it. The "Janney," "Lithoprint" and "Eure- 
ka" processes are of this nature. 



Drafting Room Geometry 

A knowledge of certain principles of geometry is essential to the 
mechanical draftsman. Purely geometrical constructions are such as 
may be made with a pair of compasses and a straight edge, but the drafts- 
man, with his instruments, has special and less laborious methods of ac- 
complishing many of these operations. For example, a line parallel to 
a given line may be constructed geometrically as indicated in Fig. 79a, 
while the draftsman's method of doing this has been shown in Fig. 7a. 



- ~ Segment 




"Sector 



Fig. 79. 



Circle. — A circle is a closed curved line every point of which is the 
same distance (radius) from a fixed point (center) within. Any two 
lines radiating from the center cut off a part of a circle (arc) and form 
an angle (Fig. 79b), each being measured in degrees, 360 of which are 
contained in a circle. Thus, a right angle is one-fourth of a circle (Fig. 
79c), or 90 degrees (90°), and may be constructed by drawing two per- 
pendicular lines (Figs. 7b and 7c). A line tangent to a circle (Fig. 79c) 
at any given point is perpendicular to a radial line through the point. 



59 



Triangles. — Plane figures having three straight sides are called tri- 
angles (Fig. 80a). The sum of the three inside angles of a triangle is 
always equal to 180°. 





a *b~ 90 ° fib* c+d+e = 180 




f=h 




Equilateral Right Scalene isosceles 

All sides equal One right angle No two sides equal Two sides equal 

(a) Triangles 




Trapezium 
No two sides parallel 



Trapezoid 
Parallelograms 



Trapezium 
No two sides parallel 




Square Rectangle Rhombus 

( b) Quadrilaterals 



Rhomboid 




Pentagon Hexagon Heptagon 

(c ) Regular Polygons 




Octagon 



Fig. 80. — Triangles, quadrilaterals and polygons. 



—Any plane figure having four straight sides is called 
The common sorts of quadrilaterals are shown in 



Quadrilaterals. - 
a quadrilateral. 
Fig. 80b. 

Polygons. — The equilateral triangle and the square are regular poly- 
gons. Other regular polygons are shown in Fig. 80c. All regular poly- 
gons can be constructed within or tangent to a circle, as is indicated in 
the case of the pentagon. 

Solids. — Some of the solids commonly used are indicated in Fig. 81. 
A sphere is a solid included within a surface which is at every point 
equidistant from an internal point (center). Both prisms (Fig. 81a) 
and cylinders have bases which are parallel and equal. When a portion 



60 



is cut away by a plane not parallel to the bases such solids are said to 
be truncated. When a cone or pyramid is similarly cut by a plane 
parallel to its base, the portion between the bases is known as a frustum 

(Fig. 81b). 









pi'! 

i 
A 

i i 




s*y 


1 

7 




\r\ \)\ 








ft 



^ Base J I 




Square (Cube) 



Vertex- ^^N 

/\\\\~Axfs 




Triangular Truncated Pentagon at /net meet 

Y 
Right Prisms 

(a) Prisms 

Vertex / tV Vertex 

/_J_£_X --Para/lei 

Bases / 





Truncated Right Frustum of Inclined Right Circular 

Square Pyramid Triangular Pyramid Cone 

( b) Pyramids and Cone 

Fig. 81. — Prisms, pyramids and cones. 

To Bisect a Line. — (Fig. 82a.) — (Geometrical Method.) Given the 
line AB. Use any radius R, with A and B as centers. Connect the arc 
intersections (C and D) with a line cutting AB at E. Then AE=BE. 
(A Draftsman's Method.) Use the triangles against a straight-edge 
placed parallel to the line (Fig. 82b), drawing three lines in the order 
indicated. Then AO=BC. 

To Divide a Line into Equal Parts. — (Fig. 83.) Given the line AB to 
be divided into seven equal parts. Select a suitable scale, placing it as 
indicated and marking the points C to 6 so as to have seven equal spaces. 
If preferred, seven equal spaces of convenient length may be stepped 
off with the dividers along any line AC. 

Draw the line BC. Then through points 1 to 6 draw lines parallel to 
BC, using the triangles (Fig. 7a). The intersections with AB will form 
the desired divisions. 

To Bisect an Angle.— (Fig. 82c.) Given the angle AOB. With 
as a center and any radius R, strike an are to obtain intersections C and 
D. With C and D as centers and any radius R._, strike arcs intersecting 
at E. Then line EO is the bisector. 



61 



To Reconstruct an Angle. — (Fig. 82d.) Given the angle AOB. Draw 
the line O'B'. With any radius B^ strike arcs from and 0'. Make 
C'D'=CD (R 2 ) and draw O'A' through D'. 



"-w * 



Hfi. 




Fig. 82. 



To Construct a Triangle. — (Fig. 82e.) Given the sides B and C as 
radii strike arcs intersecting at F. Draw DF and EF. 



.'-Line to be divided 

-t — / — t 




Scale - 



Fig. 83. — Dividing a line into a number of equal parts. 

Length of a Circular Arc. — (Fig. 84.) (First Method.) Given the 
arc AB. Draw the line BC tangent to the given arc at B (perpendicular 



62 



to the radius). Set the dividers to a suitable spacing and, starting at 
A, step off equal spaces until a point is reached just beyond B. Without 




zl^^^c 



K--- Length - 
First Method 




z>W 



^-l 



Y<-- Length ---'-» 
Second Method 



Fig. 84. — Finding the length of a circular arc. 



lifting the dividers step off the same number of spaces in a reverse di- 
rection along the tangent BC. Then BC is the required length, the 
theoretical accuracy depending on the length of the chord used. (Second 





(Long diameter given) 




(Short diameter given ) 

Fig. 85. — Construction of reguk 



(One side given ) 

• hexagons. 



Method). Draw the line B'C tangent to given arc A'B' at B'. Draw 
the chord A'B', extending it one-half its length to D. With D as a 
center and DA' as a radius strike an arc to cut the tangent line at C 
Then B'C is the required length. This construction should not be used 
when the angle AOB is greater than 60°. 



63 

The Regular Hexagon. — (Fig. 85.) There are various methods of 
constructing the hexagon. Usually the draftsman is given the distance 
across the flats or the distance across the corners, either of which may 
be used as the diameter of a circle drawn with its center at the inter- 
section of the center lines. The hexagon may then be readily constructed 
within or tangent to this circle, using the 30° -60° triangle as indicated. 
Other methods of constructing the hexagon, using only this triangle, are 
also indicated — the given dimension in each case being shown as a 
heavy line, and the sequence for drawing the lines indicated by the 
figures. 

Tangent Arcs. — (Fig. 86.) When a circular arc is tangent to a 
straight line the point of tangency will be on a line drawn through the 



Aj ~ K I + f\£ 




Centers shown thus (°) Points of tangency shown thusf**) 

Fig. 86. — Construction of tangent arcs. 



center and perpendicular to the line, and the distance of the center from 
the line will be equal to the radius. When two arcs are tangent, the 
point of tangency will be on a straight line connecting their centers, and 
the distance between the centers will be equal to the sum or difference 
of the radii. These facts form the basis of all constructions used to 
locate centers for drawing arcs. A number of such constructions involv- 
ing tangent arcs are shown in the illustration. 

The Ellipse. — (Fig. 87.) An ellipse is a closed curve so drawn that 
the sum of the distances from any point on the curve to each of two 
fixed points (foci) is the same. Each of these fixed points is called a 
focus. As every projection of a circle viewed obliquely is an ellipse, 
this curve must be drawn frequently. The major and minor axes are 



64 



usually known and may be measured off on the center lines. If desired 
the foci may be located in the manner indicated (Fig. 87a) and a suffic- 
ient number of points to define the curve located by intersecting arcs 
struck from the foci as centers. The "trammel" method (Fig. 87b) is a 
neater one for the draftsman as it requires no construction lines. On a 
straight slip of paper three points (E, F and G) are marked so that EF 
equals half the minor axis, while EG equals half the major. If the 
trammel is moved, keeping the points F and G on the major and the 



Ao^ R i +R 2 =Ma J orA x< s EFz 



n _Ma jor Axis 




Minor Axis Ma jor Axis 



_ Mpijor_ Axjs_ 

Long Diameter 




<- Point of 
Tangency 



OE=OF= Major 
Axis - Minor Axis 



(c) 



06=0H=J0E 




Fig. 87. — Construction of the ellipse and the parabola. 

minor axes, respectively, the point E will locate points on a true ellipse. 
A light line should be sketched through the series of points thus found, 
and the curve drawn in accurately with the assistance of a French curve. 

Frequently it is sufficiently accurate to approximate the ellipse by 
substituting circular arcs for the true curve. Thus, having the axis given 
(Fig. 87c), lay off OE an OF each equal to the length of the major axis 
less the minor axis. Make OG and OH each equal to three-fourths of OE. 
Use the points E, F, G and H as centers for the four circular arcs as 
indicated. 

The Parabola. — (Fig. 87d.) The parabola is an open curve so drawn 
that each point on the curve is equidistant from a fixed point (focus) 
and a straight line (directrix). Points on the curve may be found by 
assuming various values for R, as indicated in the illustration. 



LIBRARY OF CONGRESS 

iiiiiiiiiiiiiiiiiiiiH 

019 973 634 6 



LIBRARY OF CONGRESS 



019 973 634 6 # 



